The invention relates to head-up displays, and more particularly, to a sensor arrangement that ensures that a moveable portion of the head-up display is appropriately aligned.
Supplementary guidance systems such as head-up displays (HUD""s) are becoming more common in aircraft and in other applications. A HUD includes a projector assembly, typically positioned above a pilot""s head, which projects an image to a combiner. The combiner is a substantially transparent piece of machined glass that is typically secured to the interior roof of the cockpit and rotated into the pilot""s field of view when in use. The combiner is designed to reflect certain wavelengths of light such that the pilot sees an image overlaid on what is seen through the combiner (and through the cockpit window). In an aircraft application, the image may include symbols that improve the situational awareness of a pilot which enhances the operation of the aircraft.
Because symbols or other images are overlaid on what the pilot views through the cockpit window, it is important that the images reflected by the combiner toward the pilot are reflected at a precise angle. If not reflected at the proper angle, the images will not be properly overlaid onto the real world view. The angular position of the combiner is critical to the proper positioning of the reflected images. FIG. 9 depicts a combiner 10 that uses a known method of detecting whether the combiner is properly aligned. Combiner 10 includes a non-rotatable portion 12 that is secured to the interior roof of an airplane cockpit (not shown). Stationary portion 12 includes an infrared emitter 14 and a linear detector 16. A rotatable portion 18 of combiner 10 includes a support frame 20 that holds a piece of machined glass 22 in place. A mirror 24 is attached to support frame 20. Mirror 24 reflects a signal 26 from emitter 14 and directs the signal to the linear detector. The emitter, mirror and detector are aligned so that the detector will detect the signal when the rotatable portion of the combiner is properly positioned to correctly align the reflected images into a pilot""s field of vision. This method is described in greater detail in U.S. Pat. No. 4,775,218, issued to Wood et al, which is incorporated by reference herein in its entirety.
While this known method performs acceptably well, there are some drawbacks. For instance, the emitter and detector are typically not shielded from ambient light, and pulsing circuitry is therefore required to differentiate the measuring signal from ambient light. Dust may accumulate on the emitter, detector, and/or the mirror, or may otherwise interfere with signal 26, and thereby compromise the signal strength and integrity. Furthermore, it requires significant time to properly align the emitter, mirror and detector during assembly.
It is therefore an object of the invention to provide a combiner alignment detector that is shielded from ambient light.
It is another object of the invention to provide a combiner alignment detector that is simple to assemble and calibrate.
A feature of the invention is a compact detector assembly, substantially shielded from ambient light and other contaminates, that determines the correct position of the combiner by the amount of obstruction of an emitted signal.
An advantage of the invention is that proper alignment position may be inexpensively and simply determined.
The invention provides an alignment detector assembly that determines whether a first element has been moved to a predetermined position relative to a second element. The detector includes an emitter that is secured within a first optical chamber. A first optical detector is secured within a second optical chamber. The first optical chamber is optically connected to the second optical chamber such that a signal emitted from the emitter is detectable by the detector. An occluding element at least partially obstructs the signal when the first element has been moved to the predetermined position.
The invention also provides a combiner assembly for a head-up display. The combiner assembly includes a non-rotatable portion and a rotatable portion that is attached to the non-rotatable portion. The rotatable portion is selectively rotated from a stowed position to an operating position. An alignment detector detects whether the rotatable portion has been precisely rotated into the operating position. The alignment detector includes a detector housing that is secured to the non-rotatable portion of the combiner assembly, an emitter that is secured within a first chamber of the housing, and which emits a detectable signal, and a first detector that is secured within a second chamber of the housing. The first and second chambers are optically connected such that the detector detects the signal emitted from the emitter. The alignment detector also includes an occluding element that is attached to the rotatable portion. The occluding element at least partially occludes the optical connection between the first and second chambers when the rotatable portion is in the operating position.
The invention further provides a method of detecting whether a rotatable combiner for a head-up display is in a predetermined position. According to the method, a signal is emitted through a first opening and a second opening. The signal is detected after the signal has passed through the first opening and the second openings. The signal is interrupted between the first opening and the second opening when the combiner is in the predetermined position.